Various types of discrete valves have been used in the past to modulate and switch control pressure in pneumatic systems. A drawback of prior valves, however, is that they are relatively bulky and expensive, such that compact and inexpensive pneumatic control systems have not heretofore been known.
In addition, membrane switches are common in the electrical control field, being used in such familiar items as calculators, computers and appliances as well as industrial electrical control applications. The advantages of a membrane switch includes the ability to seal the switching apparatus behind the membrane and the ability to utilize compact switching components such as printed circuits and switches formed of conductive layers formed on the circuit boards.
Notwithstanding the advantages of the membrane type electrical controls, it has not heretofore been known to utilize membrane switch technology in conjunction with pneumatic controls. The result of this technology gap has been the inability to incorporate membrane switch techniques into pneumatic controllers for such items as, for example, medical devices.